WO2015082267A1 - Method for producing a power printed circuit and power printed circuit obtained by this method - Google Patents

Abstract

The invention concerns a method for producing a power printed circuit that involves providing a printed circuit comprising an insulating substrate (1) and a conductor track (4) on one of the faces of the substrate (1), and a bus bar element (5). The method involves welding the bus bar element (5) to the conductor track (4) using a laser. In order to be able to carry out the laser welding, even on a relatively thick bus bar (5), the welding is carried out on an area (7) that is thinner, relative to the maximum thickness of the bus bar. Thus, a printed circuit is obtained with a bus bar (5) with a thick area for conducting high currents and a thinner area allowing the bus bar (5) to be laser welded to the conductor track (4).

Description

 A method of manufacturing a power printed circuit and power printed circuit obtained by this method.

The invention relates to the field of power printed circuits and their manufacturing processes.

 Printed power circuits have many applications in the field of power electronics, and in particular in the automotive field. They can be used for example in converters for electric traction devices.

 A printed circuit generally comprises an insulating substrate, for example glass-epoxy, supporting a conductive layer, for example copper, in which are formed the conductive tracks of an electrical or electronic circuit. To pass strong currents in these tracks, one can consider to increase the width and / or the thickness of these tracks. But this is sometimes not enough or not compatible with the dimensions required for the circuit. Another solution is to use a plate or grid of electrically conductive material ("leadframe" according to the English terminology) or a bus bar (also called "bus bar") connected to the tracks of the printed circuit. This connection can be made by screwing, brazing, press fitting ("press fit" according to English terminology), chemical copper plating (vias) or welding. Several types of welding are envisaged in the WO document

2009/121697 Al, such as tin soldering, with solder paste or laser welding.

 An object of the invention is to provide a fast and reliable industrial process, for welding bus bars with the least possible limitations as to the dimensions thereof.

 To this end, there is provided a method for manufacturing an electrical power circuit in which, on the one hand, a substrate is provided

electrically insulating provided with a track of electrically conductive material (or conductive track) and, secondly, a bus bar. According to this method, a laser weld is produced at one or more soldering points between the bus bar and the conductive track. A thickness of the bus bar, at the weld point, less than twice the thickness of the conductive track makes it relatively easy to achieve reliable laser welding.

 This process is quite interesting industrially, as well as economically. Indeed, laser welding technology allows industrial implementation, accurate, clean, flexible, economical and with high rates. The flexibility of this technology makes it possible to adapt to many types and thicknesses of material. For example, the thickness of the conductive track may be less than 500μιη.

 The implementation of this technology can be facilitated by making a thickness restriction of the bus bar at the weld point and / or by welding a first bus bar on the conductive track whose thickness at the weld point is less than twice the thickness of the conductive track, and welding or connecting (before or after welding the first bus bar on the conductive track) at least a second bus bar on the first bus bar. For example, in this case, the first bus bar has a thickness less than or substantially equal to 400μιη and the second bus bar has a thickness greater than or substantially equal to 400μιη.

 In another aspect, the invention relates to an electric circuit obtained by this method.

 Other features and advantages of the invention will appear on reading the following detailed description and on the accompanying drawings. On these drawings:

 Figure 1 shows schematically in section an embodiment of an electric circuit according to the invention; and

 FIG. 2 is a diagrammatic sectional view of another embodiment of an electric circuit according to the invention.

 According to a first mode of implementation, the method according to the invention consists in laser welding a bus bar on a printed electrical circuit, at the level of restrictions made in the thickness of the bus bar. An example of an electric circuit obtained by this method is illustrated in FIG.

More particularly, according to this embodiment, there is provided a substrate 1 of insulating material for printed circuit. This substrate 1 may comprise one or more layers 2 of electrically conductive material. Each of these layers is based on an electrically insulating material 3. The material electrically conductive of each of the layers of electrically conductive material, and in particular of the surface layer or conductive track 4, is for example made of copper in the form of a sheet whose thickness is between 75 μιη and 105μιη. The insulating material is, for example, epoxy glass.

 A bus bar or bus bar element 5 ("bus bar" for simplicity) is then provided to be electrically connected to the conductive track 4. This bus bar is made of a material electrically good conductor copper or copper alloy or aluminum. The thickness of the bus bar is for example ΙΟΟΟμιη.

 The connection or electrical connection between the bus bar 5 and the conductive track 4 is performed by laser welding. The laser welding is carried out at one or more weld points 6. Each weld spot 6 is made at a restriction 7 of the thickness of the bus bar 5. These thickness restrictions 7 have, for example, the shape of a weld. a well or a groove, bringing the thickness of the bus bar 5, at the bottom of each restriction 7, to a thickness close to that of the conductive track 4. The ratio of one of these thicknesses relative to the other is advantageously less than two. For example, the thickness E of the bus bar 7 at the bottom of the restriction has at most twice the thickness e of the conductive track 4.

 Restrictions 7 can be made by stamping, etching, etc.

According to a variant not illustrated, the point (s) of welding are made on areas of lesser thickness (in addition to or instead of the restrictions described above) such as bevels.

 We thus mixed two technologies: that of the circuits

electric / electronic low power with that of circuits (bus bars) of high power. Thus, one obtains a circuit board with a busbar 5 with a thick zone 12, of thickness E "greater than the thickness E, to conduct strong currents and less thick zones at the level of the restrictions 7 to allow soldering by laser bus bar 5 on the conductive track 4.

According to a second embodiment, the method according to the invention consists of laser welding a bus bar on a printed circuit, and then electrically connecting the bus bar to one or more other bus bars. An example of an electric circuit obtained by this method is illustrated in FIG. As for the first embodiment, there is provided a substrate 1 of electrically insulating material, with a surface layer or conductive track 4 of electrically conductive material. One or more other layers 2 of electrically conductive material may be interposed in the thickness of the substrate 1. There is also provided a first bus bar 8 which is welded on the conductive track 4. The nature of the constituent materials

respectively of the substrate 1, the layers 2, 4 of electrically conductive material, the electrically insulating material 3 and the bus bar 5 is chosen from those mentioned in connection with the first embodiment of the method according to the invention. The first bus bar 8 is relatively thin. For example this thickness is 400μιη for a thickness of 200μιη of the conductive track 4. The thickness E of the first bus bar 8 at the welding point 6 is less than or equal to twice the thickness e of the track 4. A welding The second bus bar 9, which is thicker, is then connected to the first bus bar 8. The second bus bar 9 has, for example, a thickness E 'greater than 400 μm, for example 600μιη, or 800μιη or more. The electrical connection between the first 8 and second 8 bus bars can be achieved by welding (laser or not). The fact of not having a directly underlying fragile insulating material and / or already having a relatively thick layer of electrically and thermally conductive material (first bus bar) to evacuate the energy possibly allows to use higher energies and / or temperatures.

 Optionally, a third 10, fourth, etc. bus bar may similarly be electrically connected to the bus bars already connected to the printed circuit consisting of the substrate 1 and the conductive track 4.

 Optionally, the bus bars are stacked and fixed to each other in previous steps and a zone of smaller thickness 11 is provided to be able to perform a laser weld on the conductive track 4.

Claims

1. A method of manufacturing an electrical circuit in which an electrically insulating substrate (1) is provided with a track (4) of material electrically conductive, and a bus bar (5) and in which is welded laser, at least one weld point (6), the bus bar (5 or 8) on the track (4) of electrically conductive material,  characterized in that the thickness (E) of the bus bar (5 or 8) at the welding point (6) is less than twice the thickness (e) of the track (4) of electrically conductive material,  and in that a restriction (7) of thickness of the bus bar (5) is achieved at the point of welding (6) 2. Method according to claim 1, wherein the thickness (e) of the track (4) of electrically conductive material is less than 500μιη. 3. Method according to one of the preceding claims, wherein welding a first bus bar (8) on the track (4) of electrically conductive material whose thickness (E) at the weld point (6) is less than two the thickness (e) of the electrically conductive material track (4) and at least one second busbar (9) is welded to or connected to the first busbar (8). 4. Method according to claim 3, wherein the first bus bar (8) has a thickness (E) less than or substantially equal to 400 μιη and the second bus bar (9) has a thickness (Ε ') greater than or substantially equal to 400μιη. Electrical circuit comprising an electrically insulating substrate (1) provided with a track (4) of electrically conductive material, and a laser-welded bar bus (5 or 8), in at least one welding point (6) on the track (4) of electrically conductive material characterized in that the thickness (E) of the bus bar (5 or 8) at the welding point (6) is less than twice the thickness (e) of the track (4) of electrically conductive material, and in that the bus bar (5) has at least one restriction (7) of thickness at the weld point. 6. The electrical circuit of claim 5, wherein the thickness (e) of the track (4) of electrically conductive material is less than 500μιη. 7. Electrical circuit according to one of claims 5 to 6, comprising a first bus bar (8) soldered in at least one weld point (6) on the track (4) of electrically conductive material and whose thickness (E ) is less than twice the thickness (e) of the track (4) of electrically conductive material and wherein at least one second bus bar (9) is connected or welded to the first bus bar (8). 8. Electrical circuit according to claim 7, wherein the first bus bar (8) has a thickness (E) less than or substantially equal to 400μιη and the second bus bar has a thickness (Ε ') greater than or substantially equal to 400μιη.